Accuracy of max hill gradients using route mapping software?

[Dogtrousers]

Incidentally, having thought about it, profiles like this of mine

Are probably due to having the GPS on auto pause, and then riding up the hill so slowly that the GPS pauses, and when it wakes up again it's at a higher elevation. Must remember to switch that feature off.

I hesitate to accuse @Mr Celine of being a useless slowcoach like me, but this might also be true of the profile in this post: https://www.cyclechat.net/threads/a...g-route-mapping-software.293019/#post-7029060

 

[ColinJ]

Are probably due to having the GPS on auto pause, and then riding up the hill so slowly that the GPS pauses, and when it wakes up again it's at a higher elevation. Must remember to switch that feature off.

I had that all the time round here. It was bad enough on steep climbs but it was also doing it when I was stuck in slow-moving traffic. It has switched off and will never be switched back on!

 

[Dogtrousers]

I had that all the time round here. It was bad enough on steep climbs but it was also doing it when I was stuck in slow-moving traffic. It has switched off and will never be switched back on!

Just switched mine off. That was a challenge, finding it in the Garmin menus!

 

[Alex321]

I had that all the time round here. It was bad enough on steep climbs but it was also doing it when I was stuck in slow-moving traffic. It has switched off and will never be switched back on!

I have it turned on on my Wahoo, it isn't usually a problem, but it did think I'd stopped on *that* hill. If you don't have it turned on, then time stopped at traffic lights counts against your moving average speed I'm not actually sure why that bothers me, since I'm not competing against anybody else, but it does.

 

[Mr Celine]

Incidentally, having thought about it, profiles like this of mine
View attachment 701436

Are probably due to having the GPS on auto pause, and then riding up the hill so slowly that the GPS pauses, and when it wakes up again it's at a higher elevation. Must remember to switch that feature off.

I hesitate to accuse @Mr Celine of being a useless slowcoach like me, but this might also be true of the profile in this post: https://www.cyclechat.net/threads/a...g-route-mapping-software.293019/#post-7029060

Nowt to do with me, it was like that when I found it.
If you look at the map the segment starts between the 250m and 260m contours, which is correct. The profile shows it starting at 100feet which is wrong.
The steepest bit of that hill is actually just before the dodgy segment and is steep enough to reduce me to a useless slowcoach.

 

[Dogtrousers]

I have it turned on on my Wahoo, it isn't usually a problem, but it did think I'd stopped on *that* hill. If you don't have it turned on, then time stopped at traffic lights counts against your moving average speed I'm not actually sure why that bothers me, since I'm not competing against anybody else, but it does.

So, having switched it off, on Saturday found out why I actually do like auto pause switched on.

I like to do calculations of ETA in my head as I go along, and for this I use my moving average and throw in time for my anticipated stops then add some leeway for other minor stops and consideration for upcoming hills (or lack of them).

But if you have auto-pause off your average speed jumps all over the place every time you stop. So I ended up having to reverse engineer my moving average speed to see how I was doing "now, let's see - I stopped for about half an hour for an ice-cream, and I've had two pee stops, and there was a navigation check where I thought I'd gone wrong but hadn't ...". Good mental exercise, but I'd rather let the Garmin do it.

So I propose to switch it off for hilly rides, where it might get accidentally triggered, but on for longer rides where ETA calculations might be a factor.

 

[Ming the Merciless]

But if you have auto-pause off your average speed jumps all over the place every time you stop

Shouldn’t jump all over the place, just gradually decline whilst stopped, assuming you’re talking overall average speed. I don’t have average speed showing when riding, just my current speed plus other data such as elapsed.

 

[a.twiddler]

I do wonder how sensitive the settings are for stopping and starting, as my Etrex 20 does show moving average and total average speeds. If you're going slowly up a long hill, for example, how accurate is that? I've had a reading of 3.2 mph on a main road incline when I wasn't in a particularly low gear, and I was riding in a straight line rather than darting about as I might expect to on a LWB bike at those sorts of speeds on a real uphill.

The benefit of the Garmin is that you can swop from bike to bike without worrying about different wheel sizes. It would be interesting to use it alongside a carefully calibrated wired bike computer set accurately for the wheel size on a particular bike, to see how much it varies. With a conventional bike computer the magnet is either passing the sensor or it isn't, and once the frequency drops beyond a certain point it just shuts down. Presumably the Garmin depends on signals from satellites at intervals so its reactions to changes in speed might be less immediate.

It reads slower than the averages that I used to get with a wheel magnet bike computer. There might be possibilities that a) I've just got slower. b) It's accurate and previous bike computers have been optimistic. c) It's more accurate at higher speeds and on longer trips, not so good with shorter and slower. It does give height readings which are consistent with my starting and stopping points but in between I take it with a pinch of salt.

 

[Dogtrousers]

I just found something funny (well I found it funny anyway). Maybe "vaguely interesting only to nerds" is a better description than "funny".

There's a hill near Sevenoaks called Carter's Hill. It's a fairly hard climb. About a mile long (1.7km) about 120m (400') gain. Gradient tops out at about ~15%. The hardest section is about 50m long with an average of 13-14%. Those stats agree with how it feels to ride up, and on the OS map it has a single chevron (14-20%) It's not in the league of the hard climbs in t'North or in Wales or Scotland, but it's no picnic.

What's funny is the data that Veloviewer gives. https://veloviewer.com/segment/627137

It overstates the total elevation gain a bit (130m), that's OK, it's still the right ballpark. I'm not bothered by that. But where it gets weird is that it says that max gradient is 25.7% That's just nuts! It's nothing like that.

Just goes to show that you need to be very careful about taking these things at face value.

I spotted this because there's a sportive that takes in some of my favourite hills in the area called the Kentish Killer. I was thinking of doing it and took a look at their website and the've reproduced this 25.7% claim unquestioningly.